The present invention relates to the stabilization of aqueous solutions containing hydrogen peroxide, hydrofluoric acid and metal ions, in which solutions the hydrofluoric acid may partially be in the form of salts.
Such solutions are used especially in the surface treatment of metals, such as cleaning or chemical polishing of stainless steels.
These solutions are unstable both during use, for example in the surface treatment of metals, and when left standing, since the metal ions which they contain catalyze the decomposition of the hydrogen peroxide.
Remedies for reducing the speed of this decomposition of hydrogen peroxide in solutions of the said type have been proposed.
For example, British Pat. No. 1,164,347 proposes adding one or more saturated aliphatic alcohols to an aqueous hydrogen peroxide solution containing hydrofluoric acid and used for the chemical polishing of copper and of its alloys.
U.S. Pat. No. 3,537,926 proposes the addition of an aromatic carboxylic or dicarboxylic acid, such as benzoic acid, to the aqueous acidic solutions containing hydrogen peroxide and ammonium bifluoride, NH.sub.4 F--HF, used in polishing iron alloys.
Japanese Patent Application Japan Kokai No. 73/52,638 claims the addition of urea and of an inorganic acid to aqueous hydrogen peroxide solutions containing hydrofluoric acid or its salts and employed for polishing iron and steels.
The remedies set out above for improving the stability of solutions comprising hydrogen peroxide, hydrofluoric acid in the free form or partially combined in the form of salts, such as ammonium bifluoride, and metal ions have the disadvantage that either their economics are unattractive or that they have adverse effects on the environment.